User interaction is declining, but it's probably because Pinterest has been written about so much lately. New users are flocking to check it out who aren't part of the core demographic. Thus they lose interest quickly and leave. Before, Pinterest spread quickly among loyal users -- like moms.

Naturally, most of Pinterest's pins aren't unique. 80% are repinned, or shared on Pinterest, from someone else's Pinterest page rather than the original source.

40-60% of users still actively pin or share items on Pinterest 8 weeks after they've joined.

This chart shows pins per user based on what month that user signed up. Back in April, users were sharing more things on Pinterest, probably because the traffic was organic -- the press hadn't picked up on Pinterest yet.

By comparison, Twitter's decay rate was twice that of Pinterest's. It dropped to 20% before stabilizing.

The average new member now uses Pinterest much less than new users before. But overall, RJMetrics is impressed. "Pinterest demonstrates some of the strongest user engagement, retention, and virality metrics I have ever seen in an online business."